Planck intermediate results. XXXI. Microwave survey of Galactic supernova remnants

TL;DR

This study uses the Planck all-sky survey to detect and analyze microwave emissions from 274 Galactic supernova remnants, revealing synchrotron radiation dominance and spectral breaks likely caused by synchrotron losses.

Contribution

First comprehensive microwave survey of all known Galactic supernova remnants using Planck data, identifying emission mechanisms and spectral features.

Findings

16 remnants detected in multiple frequencies

Most emissions are from synchrotron radiation

Spectral breaks suggest synchrotron losses

Abstract

The all-sky Planck survey in 9 frequency bands was used to search for emission from all 274 known Galactic supernova remnants. Of these, 16 were detected in at least two Planck frequencies. The radio-through-microwave spectral energy distributions were compiled to determine the emission mechanism for microwave emission. In only one case, IC 443, is there high-frequency emission clearly from dust associated with the supernova remnant.In all cases, the low-frequency emission is from synchrotron radiation. A single power law, as predicted for a population of relativistic particles with energy distribution that extends continuously to high energies, is evident for many sources, including the Crab and PKS 1209-51/52. A decrease in flux density relative to the extrapolation of radio emission is evident in several sources. Their spectral energy distributions can be approximated as broken power laws, $S_\nu\propto\nu^{-\alpha}$, with the spectral index, alpha, increasing by 0.5-1 above a break frequency in the range 10-60 GHz. The break could be due to synchrotron losses.